In the recent trend of electronic appliances becoming digital and higher in frequency, the electrolytic capacitor, one of the electronic components, is required to be larger in capacity than in the conventional part and is superior in impedance characteristic in high frequency region. To meet such demand, it has been attempted to enhance the conductivity of the driving electrolyte (hereinafter called electrolyte), decrease the resistance of separator, or use a conductive compound obtained by making conductive a sheet insulator such as paper, cloth, nonwoven cloth or high polymer film, as a separator.
Also as an attempt to make the separator conductive, various methods have been proposed, such as kneading or mixing of carbon fibers or particles, and compounding with graphite powder. Moreover, by using monomer such as pyrrole, thiophen or aniline, a method of forming a conductive high polymer on the surface by chemical oxidation and polymerization is disclosed (see Japanese Laid-open Patent No. 64-90517).
In the conventional constitution, however, there was a limit in enhancement of conductivity of electrolyte, and its conductivity is at most about ten to scores of mS/cm at the present, and electrolyte having a sufficient conductivity is not developed yet, and an electrolytic capacitor of an electrolyte having a sufficient impedance characteristic is not obtained so far.
On the other hand, for decrease of resistance of separator, it has been attempted to decrease the separator thickness, lower the density, make uniform the pore size, or change from paper to high polymer nonwoven fabric, but due to lack of strength by lowering of density and other problems, a sufficient effect of lowering the resistance is not obtained yet.
Further, the separator made conductive by kneading or mixing carbon fibers or particles is not sufficient in the electric conductivity, and it was hard to obtain a separator of low density. When using a separator by compounding graphite powder, there was a problem of increase of shorting due to drop of graphite powder and dispersion into electrolyte.
On the other hand, in the method of forming a conductive high polymer on the surface by chemical oxidation and polymerization from monomer of pyrrole, thiophen or aniline, it is difficult to compose an electrolytic capacitor of which rated voltage exceeds 35 V because there is almost no effect of deterioration of dielectric oxide film by oxidizing agent or chemical formation of conductive high polymer (defect repairing capability of dielectric oxide film). If composed, however, increase of leak current or shorting between anode and cathode may occur during agent process or high temperature test.
It is hence an object of the invention to present an electrolytic capacitor of high dielectric strength excellent in impedance characteristic, leak current property and reliability.